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Cloud of anti-atoms created

Researchers at CERN in Geneva say they have made at least 50,000 atoms of cold antihydrogen, beating a rival group to the feat.

The annilihation of an antiproton with a proton (yellow) and a positron with an electron (red path) coincide, implying an antihydrogen atom Photo&colon; The ATHENA Collaboration

They hope the result will make possible detailed measurements on the atoms, which could confirm whether worlds created from matter and antimatter particles would be genuine mirror images of one another. The antihydrogen would not be a useful Star-Trek-style energy source because it would generate far less energy than is needed to create it.

For the last three years, two research groups at CERN have been racing to create large quantities of cold antihydrogen that can be closely studied. Both have had difficulty proving that what they are creating is antihydrogen, and not just a collection of the antiprotons and positrons from which these atoms are made. Now researchers from the ATHENA experiment at CERN, represented by Jeffrey Hangst of the University of Aarhus, Denmark, have published evidence of antihydrogen created in an electromagnetic particle trap.

Gerald Gabrielse, of Harvard University in the US, represents the rival ATRAP experiment and praises the sensitivity of ATHENA’s antihydrogen detector. But warns he will be checking the group’s claims carefully. “It is possible to be fooled by the subtleties of the [particle] trap,” he says.

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Annihilation event

The ATHENA experiment combines antiprotons and positrons in a magnetic and electrical trap, called a Penning trap, at temperatures of just a few degrees above absolute zero. Surrounding detectors pick up the signature of antimatter particles annihilating.

ATHENA’s claim is based on seeing events in which an antiproton and positron annihilated within millimetres of each other outside the trap. Only neutral antihydrogen atoms should be able to escape the electromagnetic trap, says Hangst.

Past experiments at ATRAP that relied on this idea were unable to distinguish between a neutral plasma of antiprotons and positrons and a cloud of antihydrogen atoms. But ATHENA also ran the experiment at a higher temperature where antihydrogen could not form and showed that the chance of a positron and antiproton escaping the trap at the same time was negligible.

The ultimate goal of both groups is not just the creation of antihydrogen, but the detection of light from antihydrogen atoms. Theorists believe the spectrum of this light should match that emitted from hydrogen atoms.

But if it does not, this could suggest that matter and antimatter are fundamentally different and could explain why there appears to be so much more matter than antimatter in our Universe.